Grant came through Pompey's youth ranks after being snapped up from highly-rated Aussie outfit ECU Joondalup.
Having made his debut for Portsmouth early in 2012 - he then enjoyed loan spells firstly with Eastleigh and then this term with Havant & Waterlooville.
His current deal was due to expire this summer, but the English-born Aussie youth defender opted to move on.
With news of Grant's availability, a host of Premier League and Championship clubs were sounding him out about his progress.
Now Sky Sports can reveal that Grant has agreed terms on a two-year deal with Stoke, who have moved quickly to secure his signature.